The present invention relates to a process for removing water moisture haze from hydrocarbon distillate oils subsequent to the steam stripping and normal process cooling of the oils.
In the refining of petroleum distillate fuel oils, the final steam stripping process produces a highly water saturated oil which, as the oil is cooled for storage, takes on a hazy or cloudy appearance due to the fact that water solubility decreases with decreasing temperature. The purpose of the steam stripping step is for the distillate fuel oil to meet a flash point temperature specification. The purchaser's specifications require that the distillate fuel oil be bright and clear in appearance.
A number of alternative methods are known and have been used to reduce the moisture content of the fuel oil product. For example, one process requires reboiling the distillate fuel while avoiding any contact with steam. Other methods use sand or filter cartridge coalescers to facilitate separation of the water droplets from the fuel oil. The product is then stored for a period of time until its appearance clears. In some cases, air is blown or bubbled through the storage tank to reduce the storage time but this step can be hazardous. Another process employs electrostatic precipitators but these devices are expensive both to install and to operate. The use of clay dessicant towers is also an expensive operation. One common technique involves the use of a salt-filled tower downstream of a coalescer. However, discharge of the salt water results in unacceptable water pollution or requires expensive water treatment while the cost of salt and the maintenance of the tower is also relatively high.
The present invention avoids the foregoing disadvantages by providing a distillate fuel oil de-watering process that is substantially less expensive to both install and operate than has been the case and which will produce a clear and bright finished fuel oil.
Normally, the water saturated fuel leaves a steam stripper in the final stage of the refining process at a temperature of between 400.degree.-600.degree. F. As the distillate is cooled to storage temperatures, solubility of the water in the fuel oil decreases and takes on the appearance of a haze due to the very fine minute droplets of water forming in the distillate oil. After cooling in the refinery process to recover the heat in the distillate fuel oil, the fuel oil is ready for treatment by the method of the present invention. Specifically, with the temperature reduced to about 120.degree.-180.degree. F., the fuel oil laden with moisture is passed through a first heat exchanger where the incoming oil is cooled by the de-watered outcoming oil being treated by the process. From the first heat exchanger, the incoming oil is passed through one or more secondary heat exchangers which may be cooled by water or air so that the oil passed through the second heat exchanger has its temperature reduced to about 80.degree.-100.degree. F. From the second heat exchanger, the cooled oil is passed through a sand coalescing vessel which is designed to effectively separate the water droplets from the fuel oil. From the sand coalescer, the recovered oil, as noted above, is passed back through the first heat exchanger to raise its temperature to a range of between 100.degree.-120.degree. F. before sending the fuel oil to storage. Water from the sand coalescer vessel is discharged to drain.
It will be appreciated that the process can be run, after installation, with only the minor additional cost of supplying a cooling fluid to the second heat exchanger device and periodic cleaning or replacement of the sand in the sand coalescer vessel.
Additional advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: